JeffGrice

Hi,

I've read a couple of posts that suggest you can't simply hook up the timing light and check timing at idle on 454 mag efi motors.

I also read you need a special timing light that plugs into the ignition system.

Can someone pls help me with the proper procedure. My 454 mags are 1995.

Thanks!

Jeff

H2Xmark

you need to put the computer in field service mode, you can use any timing light, to put in field service mode you need to open the metal E.C.M. box on top of the left side valve cover/exhaust manifold, when you open the box[also has engine#,transom# and drive# decal on top of it] you will find a connector in there with a plug on it, the plug has a plastic lead to keep you from loosing this item, it is only there to keep out dirt and such, unplug this cap and jump the two end wires that are black and black/white, that will be diagnostic lead to ground, then set your timing to spec, after you are done remove the jumper, merc also makes a factory tool to jump this connection its about 9 dollars but you can use some wire to get the job done

JeffGrice

Thanks for the detail instructions!

Jeff